Upgrading of reformate with a tellurium-faujasite catalyst

ABSTRACT

NAPHTHA IS REFORMED OVER A NOBLE METAL CATALYST TO EFFECT A DESIRED DEGREE OF NAPHTHENE AROMATIZATION AND THEN SUBJECTED TO A POST-REFORMING STEP IN WHICH PARAFFINS IN THE REFORMATE ARE AROMATIZED OVER A DEHYDROCYCLIZATION CATALYST.

y 1972 R. J. MIKOVSKY ET AL 63,426

UPGRADING OF REFORMATE WITH A TELLURIUM-FAUJACITE CAT Filed Nov. 14,1969 ALYST 6 Sheets-Sheet 3 FIGURE 5 POST-REFORMING OVER13X-TeCATALYSTOFEXAMPLE I Liquid-Yield Octane-Number Relationship Octane Number hwan/orsfP/ChO/d .1 M/kOI/S/Q/ Ammo/7y J. S/Wes/r/ Robe/f L. 5/27/77) y 16, 1972R. J. MIKOVSKY ETAL 3,663,426

UPGRADING OF REFORMATE WITH A TELLURIUM-FAUJACITE CATALYST Filed Nov.14, 1969 6 Sheets-Sheet 4 LL. 0 O C\] L0 in F l GU R E 4 Oc'rone Numbersof Liquid Products Tlme -on- Stream hrs POST-REFORMiNG OVER 0 9 A|2 O3CATALYST OF EXAMPLE 2;

LL. 0 0 L0 00 O O 10 0 LO 0 9 9 m m g +5 1aqwn auop mum/0r; fP/chard J.M/kov: /r An/hO/U/J. S/fi/es/r/ R006 L. Sm/f/i May 16, 1972 Filed NOV.14, 1969 Liquid Yield,wf."/

R. J. MIKOVSKY ET AL 3,663,426

UPGRADING OF REFORMATE WITH A TELLURIUI/I-FFUJAITTE CATALYST 6Sheets-Sheet 6 YIELD ADVANTAGE: PLATINUM REFORMING ALONE VERSUS PLATINUMREFORMING FOLLOWED BY POS'F I REFORMING TO SAME O.N.

. Combination Process Platinum Reforming 85 9O 95 I00 I05 IIO OctaneNumber,R+ 3

/n van/0r; mam/a M/kol/s/ry Ammo/7y J Sf/vesfr/ 9008/) L. Sm/fh UnitedStates Patent Oflice 3,663,426 UPGRADING F REFORMATE WITH ATELLURIUM-FAUJASITE CATALYST Richard J. Mikovsky, Trenton, N..I.,Anthony J. Silvestri,

Morrisville, Pa., and Robert L. Smith, Hopewell, N.J.,

assignors to Mobil Oil Corporation Filed Nov. 14, 1969, Ser. No. 876,624Int. Cl. Cg 39/00 US. Cl. 208-65 9 Claims ABSTRACT OF THE DISCLOSURENaphtha is reformed over a noble metal catalyst to effect a desireddegree of naphthene aromatization and then subjected to a post-reformingstep in which paraffins in the reformate are aromatized over adehydrocyclization catalyst.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to a reforming process, and in particular to a combinationreforming process designed to improve yields by taking advantage of theselective dehydrocyclization capability of non-noble metaldehydrocyclization catalysts.

Description of prior art The low-octane character of parafiins,especially nparaflins, relative to aromatics has long been recognized,and various proposals have been advanced for removing n-parafiins fromreformate to yield a gasoline having a higher octane rating than thereformate. In US. Pat. 2,952,014 it is proposed to selectively sorbn-paraffins out of reformate by contacting the reformate with amolecular sieve capable, by reason of its pore size, of sorbing noreformate components other than n-parafiins. In British Pat. 1,129,381the reformate is subjected to hydrocracking over a similarlysize-selective molecular sieve catalyst, with the consequence thatn-parafiin, and no other reformate component, is converted to easilyseparable material.

SUMMARY OF THE INVENTION According to the present invention reformateobtained by subjecting a naphtha, under reforming conditions, to theaction of a noble metal reforming catalyst is contacted in apost-reforming operation with a dehydrocyclization catalyst wherebyparaffins in the reformate are converted to relatively high-octanearomatics with better selectivity than the noble-metal catalyst.

DESCRIPTION OF SPECIFIC EMBODIMENTS The reforming catalyst is preferablya conventional platinum-on-alumina catalyst typically containing 0.3-0.6% weight platinum and up to about 1% weight halogen, preferablychloride. The conditions of contact between the naphtha feed and thecatalyst usually comprise a temperature in the range 600' to 1000" F., apressure in the range 1-00 to 1000 psi, a liquid hourly space velocityin the range 0.1 to 10 and an H /HC mol ratio in the range 1 to 20. Thereforming may be carried out as a listed bed, moving bed or fluidizedbed operation, although for purposes of brevity it will be described inthis specification principally in terms of a three-reactor fixed bedinstallation.

As is known, the principal reactions brought about by reforming over aplatinum catalyst are dehydrogenation of cyclohexanes to aromatics,isomerization of alkylcyclopentanes to cyclohexanes, isomerization anddehydrocyclization of paraffius and, inevitably and undesir- 3,663,426Patented May 16, 1972 ably, some cracking. As the severity of thereforming operation increases, the extent to which all these reactionsproceed increases, with the consequence that the liquid yield falls (dueto the destruction of normallyliquid components by the cracking) whilstthe octane number of the liquid product rises. A compromise musttherefore be effected in selecting conditions of reforming, the acceptedproduct octane value being determined by the yield loss which can betolerated.

According to the present invention, the need for such a compromise islargely eliminated by conducting the reforming at relatively lowseverity, whilst still permitting substantial progress of thoseoctane-increasing reactions particularly effectively catalyzed byplatinum. In particular, conversion of both 5- and 6-membered naphthenesto aromatics is permitted to go to substantial completion (naphtheneextinction). The reformate is then subjected to a post-reforming step inwhich the paraffin component of the reformer charge, which component hasbeen less modified by the reforming conditions, is dehydrocyclized toaromatics.

The catalyst used in the post-reforming step is one having highselectivity for dehydrocyclization of paraffins, which have at least 6consecutive carbon atoms. The preferred catalysts are chromia-aluminaand tellurium-impregnated synthetic faujaste, but other catalysts havingdehydrocyclization activity such as the oxides of molybdenum, tungsten,vanadium, cerium, thorium, neodynium and samarium, and mixtures of oneor more of these may be employed (in association with a suitablecarrier, such as alumina).

In the presently preferred manner of practising the invention, thenaphthene-depleted reformate, optionally after deisohexanization and/orstabilization by C -hydrocarbon removal, is subjected to a single-pass,fixed-bed contact with the dehydrocyclization catalyst, that catalystbeing either a Cr O /Al O catalyst typically containing about 10% weightCr O on a support of 'y-alumina; or being an alkali-metal form, such asthe sodium form, of zeolite X loaded with 6% by weight (of thecomposite) of tellurium.

The extent to which the reformate is depleted in naphthenes may, asmentioned above, amount to naphthene extinction; but a small naphthenecontent can be tolerated in the post-reforming stage. Thus we haveachieved excellent post-reforming stage performance with a reformatehaving a naphthene content of 1.5%, although at naphthene contents ofthe order of 10% performance falls off badly. The precise extent towhich residual reformate naphthenes affect post-reforming performancedepends, naturally, on the particular conditions selected for theparticular post-reforming operation.

Best results are obtained by operation at a temperature in the range 850to 1100" F., a liquid hourly space velocity in the range 0.05 to 2.0,and under a hydrogen pressure in the range 0.1 to 5.0 atm. Theselectivity for dehydrocyclization of the preferred catalysts is at itshighest at a prevailing hydrogen pressure of 1 atm. or less, and thehydrogen pressure applied in the post-reforming step is therefore suchas will, after taking account of reactor back-pressure, provide forcontacting of catalyst and reformate at a pressure of about 1 atm. in atleast part of the catalyst bed.

BRIEF DESCRIPTION OF THE DRAWING Referring to FIG. 1, a reforming unitcomprising stages 1, 2, and 3 is supplied with naphtha reformer feed vialine 4; the feed is introduced into reformer stage 1 together withrecycle hydrogen supplied via line 5. The effluent from reformer stage3, typically at a temperature of 900 F, is subjected to separation (Hfrom reformate) at reformer pressure in high pressure separator 6;

the H is recycled. The liquid product from high pressure separator 6 isfed to stabilizer 7, in which normally gaseous hydrocarbons, includingbutane, are flashed off. The stabilized reformate is then optionally ledto distillation column 8 in which hydrocarbons boiling below n-hexaneand having less than the succession of 6 carbon atoms required fordehydrocyclization are fractionated off. The liquid product from thedistillation is then fed to postreforming reactor 9 and thepost-reforming product from that reactor-characterized by substantialreplacement of feed paraffins by aromatics-As taken off via conduit 10.

In order that the invention may be still more clearly understood, thefollowing examples are provided by way of illustration of preferredembodiments.

EXAMPLE 1 A C -290" F. Kuwait naphtha, analyzing 8.1 wt. percentaromatics, 1712 wt. percent naphthenes and 74.7 wt. percent parafiins,was passed under reforming conditions (900 F. inlet, 250 p.s.i.g., 1.2LHSV, and 7.5 H /HC mol ratio) through a three-reactor reformer incontact with a commercial reforming catalyst. The catalyst comprised0.35% weight platinum on a support of eta alumina and had a surface areaof 377 rnF/gm. and a chloride content of 0.42% weight. The raw liquidproduct had an octane number (C +(R+3)) of 94.5, and contained 1.5 wt.percent naphthenes and 36.4 wt. percent aromatics. Octane number wasdetermined in accordance with ASTM standard D-2699-68.

The post-reforming was conducted at a liquid hourly space velocity of0.10, a temperature of 850 R, an H /hydrocarbon mol ratio of 4.0, and anoverall pressure approximately atmospheric. The catalyst was prepared byball milling together, for 4 hours, Linde Zeolite 13X (sodium form) andelemental tellurium in proportions calculated to yield a compositecontaining about 6 wt. percent Te. The composite was pretreated for 18hours in flowing hydrogen at 1000 F. before use. A chromatographicanalysis of the charge and of the liquid products at various timeintervals is presented in Table I, whilst data regarding the octanenumber of liquid product is presented in Table II. Information fromthese tables is represented graphically in FIGS. 2 and 3, which show,respectively, Aromatics Content and Octane Number versus Time and LiquidYield/Octane Number Relationship.

From these data, it is clear that a surprising upgrading of thereformate, at rather high yield, was effected during the first fewperiods of on-stream time, the catalyst re quiring regeneration after20-25 hours service.

Additional runs performed with the same charge stock and otherwiseidentical conditions indicated that catalyst aging is decreased byhydrogen dilution of the charge and also by operating at relatively lowtemperatures.

EXAMPLE II Using the same charge stock as in Example I, and carrying outthe initial reforming under the same conditions as in that example, apost-reforming operation was carried out using, in contrast to thetellurium catalyst of that example, a chromia-alumina catalystcontaining 10.4% Cr o 0.44% K 0 and 0.39% CeO and made by method ofArchibald and Greensfelder. The post-reforming was carried out underconditions of space velocity, pressure and hydrogen dilution the same asthose of the postreforming of Example I, but three runs were made, attemperatures of 850, 900 and 950 F., respectively. The relationshipbetween octane number of liquid product and time-on-stream is shown inFIG. 4. The relationship between liquid yield and product octane numberis shown in FIG. 5. Consideration of these two figures shows, as mightbe expected, that increasing octane number is associated with increasingseverity of operation and with decreased liquid yield. However, despitethe loss of liquid yield and expense of the increased severity theoperations shown in FIGS. 4 and 5 compare highly favorably with astraight reforming operation devoid of any post reforming step.

This favorable comparison is illustrated in FIG. 6 in which the fall-01fin liquid yield associated with the increasing severity necessary toattain a given octane value product is shown to be far less marked for acombination process in accordance with the invention than forPt-reforming alone. Typical analyses conforming with the curves of FIG.6 are shown in Table III in respect of two target octane values, viz 100and 105 (both leaded research octane values, 3 cc. TEL/US gal.).

Archibald, R. 0., and Greensfelder, B. S., Ind. & Eng. Chem., 37, 356(1945).

TABLE I.POST-REFORMING OVER l3X-Te CATALYST OF EXAMPLE I-CHROMATOGRAIHIG ANALYSES OF CHARGE AND LIQUID PRODUCTS Sample Charge 1-4hrs. 4-7 hrs. 7-10 hrs. 10-13 hrs. 13-16 hrs. 16-19 hrs. 19-22 hrs.

Weight percent:

r-C5 8. 4 10. 7 13. 3 12. 8 10. 9 10. 9 8. 3 9. 5 0+6 nonaromatlcs--.-55. 2 20. 9 25. 0 31. 6 38. 9 42. 9 47. 7 47. 3 Benzene 4. 6 12.8 11. 210. 6 7. 8 6. 5 6. 3 6. 0 Toluene 14. 4 36. 1 29. 5 24. 4 21. 5 19. 717. 6 17. 1 Cr aromatics.--- 13. 9 17. 8 18. 6 18.0 17. 8 16. 8 16. 815. 9 Ce aromaties...- 3. 5 1. 7 2. 4 2. 6 3. 1 3. 3 3. 3 4. 2

TABLE III.COMPARISON OF PIC-REFORMING ALONE WITH Pt-REFORMING COMBINEDWlTl-I Ct Og/Al O;

POST-REFORMING Pt- Combinarefermlng tion process A TABLEII.POS'I-REFORMING OVER g gg g isgf 1 2 2 1 +0 9 13X-Te CATALYST orEXAMPLE I 31 M 4 OOTANE NUMBERS (n+3 OF LIQUID 01-05, wt. percent .2 Iis. 9 910 -4I 9 P ROD UCTS 1%, wtt. percentnu 1 -1. 7 n 4, w .percen .6l.5 Tl g g 0+5, Wt.percent.. 76. 0 82.8 +0. 8 h me N c 3118 05+,v0l.pereent. 71. 7 l 78. 1 +6.4 rs umber 1r. 0+. ON(R+3) =1 :mkWt.rgercentni; 1. 4 3.2 i1. 6 o e, w pereen 0 0. 0. 4 i; 2 C1-C3, wt.pereent.. 20. 8 l1. 7 9. 1 7 I 104, wt.percent 6.9 3.1 --3.8 10 g n04,wt percent-.. 5.6 2. 5 -3. 1 13 1 8 0+5, wt.pereent 65.3 79. 3 +14. 0 80+5, vol percent 59. 9 1 72. 7 +12. 8 19-22 95. s

l Gravities were estimated It can be seen from the close coincidencebetween those curves of FIG. 5 which show post-reforming over achromia-alumina catalyst and that which shows post-reforming over a13X-Te catalyst that the comparison depicted in FIG. 6 holds goodirrespective of which of the preferred catalysts is employed for thecombination process.

It will therefore be appreciated that by means of the invention thethree-fold advantage is achieved that (i) the initial platinum reformingstep need only be conducted at the severity necessary to achievesubstantial, preferably complete, conversion of naphthenes, thusprolonging reforming catalyst life; (ii) the paraflins, which arepermitted largely to survive this reforming, are more selectivelyconverted into desired high-octane gasoline components than by straightreforming; and (iii) the diminution in yield associated with the priorart practices of simply separating off the reformate paraflins, orconverting them to nongasolen products, is avoided.

What is claimed is:

1. Reforming process comprising contacting a charge naphtha, underreforming conditions, with a platinum metal-containing reformingcatalyst until at least a major portion of the naphthenes have beenaromatized in said charge, the resulting reformate being then contactedwith a tellurium-impregnated synthetic faujasite aromatization catalyst,to increase the octane number of said reformate by aromatization ofparafiins, at a temperature in the range 800 to 1100 F., a liquid hourlyspace velocity in the range 0.5 to 2.0 and a hydrogen partial pressurein the range 0.1 to 5.0 atmospheres.

2. Process according to claim 1 wherein the faujasite is an alkali-metalfaujasite.

3. Process according to claim 2 wherein the aromatization catalystcontains about 1 to 11 weight percent tellurium.

4. Process according to claim 3 wherein said catalyst contains about 6Weight percent tellurium.

5. Process according to claim 1 wherein the synthetic faujasite iszeolite. X.

6. Process according to claim 3 wherein the aromatization catalyst ispretreated in flowing hydrogen at about 1000 F. before use.

7. Process according to claim 1 wherein said resulting reformatecontains no more than about 1.5 weight percent naphthenes.

8. Process according to claim 1 wherein said hydrogen partial pressureis no more than 1.0 atmosphere.

9. Process according to claim 1 wherein the hydrogen/ hydrocarbon molratio during said aromatization of paraffins is about 4.0.

References Cited UNITED STATES PATENTS 2,758,062 8/ 1956 Arundale et al.20865 3,179,602 4/ 1965 Gremillion 252-465 7/1968 Pfefferle 20865FOREIGN PATENTS 5/1961 Canada 20865 8/1961 Canada 20865 HERBERT LEVIN-E,Primary Examiner

